The present invention relates to a method and a control device for controlling the waste heat generated by a motor vehicle with an electric drive, wherein the electric drive has at least one rechargeable battery and an electric machine for driving the motor vehicle.
Motor vehicles that are operated exclusively electrically over long periods of travel include electric heating devices for heating the interior because the heat loss of the electric drive train, for example the rechargeable battery (high voltage battery), the electric machine, the power electronics, the direct current/direct current converter and the like is not sufficient in all driving situations to heat the interior of the motor vehicle. Such an additional electric heating device requires additional installation space, increases the cost of the motor vehicle, and increases the weight of the motor vehicle.
It is known from DE 10 2012 019 005 A1 to use the waste heat of the electric machine and the electric actuator for heating the interior of a motor vehicle.
EP 1 313 628 B1 discloses the operation of an electric machine of a motor vehicle outside of the optimum operating point to increase the heat loss and control the temperature of the interior.
The service life of an electric component depends, among other things, on the temperature of the component during operation. Temperature fluctuations of the components of an electric drive can also reduce the service life of the components.
The object of the invention is to provide an improved method and an improved control means to control the waste heat generated by a motor vehicle with an electric drive.
The object of the invention is attained with a method for controlling the waste heat, a computer program, a waste heat control system and a motor vehicle having such a waste heat control system, in accordance with embodiments of the invention.
The method according to the invention for controlling the waste heat generated by a motor vehicle with an electric drive, wherein the electric drive comprises a rechargeable battery and an electric machine for driving the motor vehicle, includes the act of determining the thermal load of at least two components of the electric drive. If a first electric component of the electric drive has a lower thermal load than a second electric component, the electric drive is actuated in such a way that the generation of waste heat in the first electric component of the electric drive increases and the generation of waste heat in the second electric component of the electric drive does not increase, and preferably decreases. If the second electric component of the electric drive has a lower thermal load than the first electric component, the electric drive is actuated in such a way that the generation of waste heat in the second electric component of the electric drive increases and the generation of waste heat in the first electric component of the electric drive does not increase, and preferably decreases.
The term “thermal load” may include a temperature of the electric component, the integral of the temperature of the electric component over time, a difference to the maximum allowable temperature, a combination of said quantities, any other thermal quantity and/or any combinations of thermal quantities. The electric drive comprises the rechargeable battery, the electric machine that is supplied with current by the rechargeable battery and drives the motor vehicle, and a drive control device that controls the actuation of the electric machine with current from the rechargeable battery and/or controls the charging of the rechargeable battery with current generated by the electric machine. The drive control means can comprise a direct current/direct current converter with a plurality of power transistors, a link capacitor, plugs, lines, a semiconductor-actuation, capacitors, diodes, and other passive components.
The method can also include the step of requesting heat for controlling the temperature of the interior. Subsequent thereto, the thermal load of at least two components of the electric drive is determined. Furthermore, the method can include the step of controlling the temperature of the interior of the motor vehicle with the waste heat generated by the components of the electric drive.
The method also includes the step of increasing the switching frequency of at least one of the transistors of the control device if more waste heat is to be generated in the drive control device and less waste heat is to be generated in the electric machine. Furthermore, the method may include the step of reducing the switching frequency of at least one of the transistors in the drive control device if less waste heat is to be generated in the drive control device and more waste heat is to be generated in the electric machine. The switching frequency is the frequency that generates the sampling points of the current signal, which form the current signal that is delivered to the electric machine.
Usually, the switching frequency of the transistors can be set between 5 kHz and 10 kHz. Generally, a lower switching frequency is used at lower speeds, and a higher switching frequency is used at higher speeds.
The method can also include the step of monitoring the temperature of the drive control device and the actuation of the electric drive in such a way that the fluctuation of the temperature of the components of the drive control device is lower than a predetermined threshold value. This ensures that temperature fluctuations of the components of the drive control device are avoided, which can increase the service life of the components of the drive control device and the drive control device as such overall.
The method can also include the step of supplying current by the drive control device in such a way that the ratio of the field-generating current id and the torque-generating current iq is outside of the optimum ratio of the field-generating current id and the torque-generating current iq for the respective operating point. In particular, increasing the field-generating current id leads to more dissipation power in the electric components of the drive control device. By impressing current that does not have the optimum ratio of the field-generating current id and the torque-generating current iq, the temperature in the electric machine as well as the temperature of the components of the drive control device is increased.
According to another aspect of the invention, it is possible to combine two measures. If more dissipation power is to be generated overall to control the temperature of the interior of the motor vehicle, a first method step can be performed, in which less waste heat is generated in one component of the electric drive, for example by changing the switching frequency. Then a second method step can be performed, which generates more waste heat in at least two components of the electric drive. In this way, it is possible to control the generation of waste heat in such a way that in the component in which less waste heat is generated because of the first method step, essentially the same waste heat is generated again as prior to the first method step to reduce the waste heat generated by the first component. This makes it possible to increase the service life of the components because they are operated at a constant temperature as much as possible.
The method can furthermore include the steps of applying a brake of the motor vehicle and the actuation of the electric drive in such a way that it is to move the motor vehicle. The emergency brake supports the torque generated by the electric machine. The torque tensions the power train. This results in only slight noise because there is no rotation and a constant torque is applied. Because of the limited holding torque of the emergency brake, for example of approximately 50 Nm to approximately 100 Nm, the maximum torque of the electric machine is limited. Because of the direct current load during standstill, the limiting continuous withstand power of the electric machine and the drive control device decreases. When the brake is released inadvertently or if the holding force is exceeded, for example with a downhill grade, an undesired acceleration of the motor vehicle may occur. Because of a potentially irregular heating, temperature sensors, for example the temperature sensors of the winding, cannot record especially hot spots. This aspect of the invention is suitable for a preconditioning of the interior or for heating the interior in case of a traffic-related stoppage of the vehicle, for example at a traffic light.
The method can also include the step of actuation of the drive control device in such a way that only a field-generating current id is supplied to the electric machine. The field-generating current id does not contribute to the torque delivered by the electric machine. There is only low noise because no rotation occurs. Because of the direct current load during standstill, the limiting continuous withstand power of the electric machine and the drive control device decreases. Because of a potential irregular heating, the temperature sensors of the winding do not detect especially hot spots. This step is feasible for preconditioning the interior during standstill of the motor vehicle or during traffic-related stoppage of the motor vehicle.
The method can include the step of actuation of the electric drive in such a way that the drive control device actuates the electric machine such that a rotating field is created in the electric machine without the axis of the electric machine rotating. The frequency of the rotating field can be so high that it cannot effect a rotation of the axis of the electric machine because the generated torque is too low. This step can result in strong high-frequency alternating torques. Possibly, vibrations and/or noises may be expected because of the alternating torques. The system is outside of the regular current control. The waste heat and/or the losses are therefore difficult to estimate. Loss maximization due to a symmetrical load and frequency-related iron losses is possible. Furthermore, it is necessary to switch the heating operating mode to normal control during driving of the motor vehicle. This step is suitable for preconditioning the interior of the motor vehicle and in case of a traffic-related stop of the motor vehicle.
According to another aspect of the invention, if the electric machine and/or the motor vehicle is at a standstill, the electric drive can be actuated such that the drive control device actuates the electric machine in such a way that the electric machine generates a first torque in a first direction and then a second torque in a second direction that is opposite to the first direction. The motor vehicle is not moved from the place where it is located by the first torque and the second torque. So as to avoid a rotating movement of the motor vehicle's power wheel, the control must quickly reverse the torque direction. Oscillations may occur due to dynamic torque changes. Because the torques are built up and relieved dynamically, a constant working point and/or loss value cannot be set. Depending on the dynamics of the control, a movement of the motor vehicle is possible. This aspect of the method can be applied for preconditioning the interior during parking of the motor vehicle or during traffic-related stopping. Furthermore, this operating mode can be used with an initial electric trip, e.g. after prolonged parking of the vehicle.
Under a further aspect, the invention includes the actuation of the electric drive, if the vehicle is moving such that the drive control device actuates the electric machine such that the electric machine generates a first superimposed torque in the first direction and then a second superimposed torque in the second direction, which is opposite to the first direction. The first superimposed torque and the second superimposed torque are superimposed on a torque of the electric machine. The motor vehicle is not accelerated and not decelerated by the first superimposed torque and the second superimposed torque. High-frequency alternating torques are superimposed on the driving torque and/or a coasting to generate additional losses. In doing so, there is the risk of creating a mechanical oscillation in the drive train. The alternating torques are critical with respect to control engineering.
Under a further aspect of the invention, if a transmission of the motor vehicle is in idle so that no torque is transmitted from the electric machine to a power wheel, the electric drive can be actuated such that the drive control device actuates the electric machine in such a way that the electric machine generates a torque. The electric machine can rotate the drive axis at a low speed. Oscillations and noises may occur due to the rotation. Losses can be set up to the maximum current for each speed. A bearing lubrication must be ensured, even in the case of parking. After the preconditioning, the axis of the electric machine must be brought to a standstill. This aspect of the invention is applicable for preconditioning the interior as well as for heating because of a traffic-related stop.
According to a further aspect of the invention, if the electric machine generates a torque for driving the vehicle, the electric drive can be actuated such that the drive control device delivers a higher field-generating current id to the electric machine than is required for the respective operating point of the electrical machine. Especially when starting, it is possible to heat for a short period of time with the maximum possible waste heating. The additional field-generating current id is superimposed on the regular control.
According to another aspect of the invention, if the electric machine generates current, the electric drive can be actuated such that a higher field-generating current id flows from the electric machine to the drive control device.
The invention also relates to a computer program product, which, if it is loaded into a memory of a computer having a processor, executes the steps of the method described above.
The invention also relates to a waste heat control system for a motor vehicle having an electric drive, which comprises a rechargeable battery and an electric machine that is supplied with current by the rechargeable battery and drives the motor vehicle. The waste heat control system is designed to determine the thermal load of at least two components of the electric drive. If one electric component of the electric drive has a lower thermal load than a second electric component, the electric drive is actuated such that the generation of waste heat increases in the first electric component of the electric drive and the generation of waste heat in the second electric component of the electric drive does not increase, and preferably decreases. If the first electric component of the electric drive has a higher thermal load than the second electric component, the electric drive is actuated such that the generation of waste heat in the second electric component of the electric drive increases and the generation of waste heat in the first electric component of the electric drive does not increase, and preferably decreases. The waste heat control system can be modified in such a way as described earlier with respect to the method.
The invention also relates to a motor vehicle with the waste heat control system described earlier.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.